# Water immersion: increase DOF

Discussion in 'Digital Photography' started by Harold keller, Dec 28, 2009.

1. ### Harold kellerGuest

Someone once told me that one effect of photographing live fish in a
glass aquarium is that the refractive index of the water somehow
increases the depth of field.

Has anyone else heard of this? Does it sound plausible?

Harold Keller

Harold keller, Dec 28, 2009

2. ### Eric StevensGuest

On Mon, 28 Dec 2009 20:36:02 GMT, (Harold
keller) wrote:

>Someone once told me that one effect of photographing live fish in a
>glass aquarium is that the refractive index of the water somehow
>increases the depth of field.
>
>Has anyone else heard of this? Does it sound plausible?

The speed of light in water is less than it is in air. The effect is
to longitudinally compress the geometry of light rays in front of the
lens. Everything gets compressed, including the depth of field.

As far as your question goes, the actual depth of field is reduced but
the apparent depth of field is increased. I am sure that answer will
leave you increasingly confused.

Eric Stevens

Eric Stevens, Dec 29, 2009

3. ### NameHereGuest

On Tue, 29 Dec 2009 21:39:08 +1300, Eric Stevens <>
wrote:

>The speed of light in water is less than it is in air.

Which leads to the question, how can the speed of light ever be used as a
mathematical constant? Since there's no such thing as a perfect vacuum,
there's no such thing as the constant "C" known as the speed-of-light. It's
all opinion, no matter which way you look at it.

NameHere, Dec 29, 2009
4. ### Ray FischerGuest

NameHere <> wrote:
>On Tue, 29 Dec 2009 21:39:08 +1300, Eric Stevens <>
>wrote:
>
>>The speed of light in water is less than it is in air.

>
>Which leads to the question, how can the speed of light ever be used as a
>mathematical constant? Since there's no such thing as a perfect vacuum,
>there's no such thing as the constant "C" known as the speed-of-light. It's
>all opinion, no matter which way you look at it.

LOL! So if your opinion is that the speed of light is 1000mph then it
must be so? You're pretty silly.

--
Ray Fischer

Ray Fischer, Dec 29, 2009
5. ### Harold kellerGuest

>>Someone once told me that one effect of photographing live fish in a
>>glass aquarium is that the refractive index of the water somehow
>>increases the depth of field.
>>
>>Has anyone else heard of this? Does it sound plausible?

>
>The speed of light in water is less than it is in air. The effect is
>to longitudinally compress the geometry of light rays in front of the
>lens. Everything gets compressed, including the depth of field.
>
>As far as your question goes, the actual depth of field is reduced but
>the apparent depth of field is increased. I am sure that answer will
>leave you increasingly confused.
>
>
>
>Eric Stevens

Do you mean it is reduced within the water, but appears greater from
outside the aquarium/water?

On a practical level, if my camera is outside of the aquarium, and I
am photogrpahing fish swimming inside it, does the DOF become less
critical, or increased, in proportion to the refractive index of
water?

Harold Keller

Harold keller, Dec 29, 2009
6. ### NameHereGuest

On Tue, 29 Dec 2009 13:34:37 GMT, (Harold keller)
wrote:

>>>Someone once told me that one effect of photographing live fish in a
>>>glass aquarium is that the refractive index of the water somehow
>>>increases the depth of field.
>>>
>>>Has anyone else heard of this? Does it sound plausible?

>>
>>The speed of light in water is less than it is in air. The effect is
>>to longitudinally compress the geometry of light rays in front of the
>>lens. Everything gets compressed, including the depth of field.
>>
>>As far as your question goes, the actual depth of field is reduced but
>>the apparent depth of field is increased. I am sure that answer will
>>leave you increasingly confused.
>>
>>
>>
>>Eric Stevens

>
>
>Do you mean it is reduced within the water, but appears greater from
>outside the aquarium/water?
>
>On a practical level, if my camera is outside of the aquarium, and I
>am photogrpahing fish swimming inside it, does the DOF become less
>critical, or increased, in proportion to the refractive index of
>water?
>
>Harold Keller

Let's see if we can explain this in a way you'll understand.

Anything within the water will have the distances between them
foreshortened. Meaning, all subjects within the water will appear closer
and more compressed, back to front.

Let's, for the sake of argument, suppose you have set your camera to have a
useful DOF of 3 ft. for your chosen subject distances, of 2 to 5 ft. away
from your camera lens. Outside of that aquarium all subjects from 2 to 5
ft. will be in useful focus. Let's say the aquarium itself is 3 ft. in
depth, front to back. But due to the refraction of water it will appear to
have a depth (front to back) of only 2 ft. (Slight exaggeration for
explanation only.) Therefore, everything within that tank will be in focus,
as well as anything one foot in front of the tank will still fit within
your 3 ft. DOF range (you still have 1 ft. of DOF to use up, 2+1=3). In
effect, you are now getting a 4 ft. DOF range because 3 ft. of the
available distance has been compressed to a 2 ft. depth by the refraction
of water.

It matters not if your camera is within the water or outside of the water.
What matters are any subjects within the water. All of them will appear to
have their distances between each other more compressed, compared to the
same distances they would all have outside of the water. Therefore, the
useful DOF set by your camera's optics becomes less critical for all
subjects within the water.

On an even more practical level, I have photographed many fish in aquariums
in the past (as well as in their native environments). Never did I concern
myself with this issue because it's all relative to each subject, framing,
distance, and light levels at the time for each photograph, no two
circumstances ever the same. I just previewed the DOF in my viewfinder,
selected a useful aperture, and took their images. Are you asking this
again because you really have a need for this information and truly can't
grasp what is happening? Or are you just another troll thinking up silly
questions and feigning stupidity for the attention it will bring to you.

NameHere, Dec 29, 2009
7. ### ChrlzGuest

On Dec 29, 6:39 pm, Eric Stevens <> wrote:
> On Mon, 28 Dec 2009 20:36:02 GMT, (Harold
>
> keller) wrote:
> >Someone once told me that one effect of photographing live fish in a
> >glass aquarium is that the refractive index of the water somehow
> >increases the depth of field.

>
> >Has anyone else heard of this? Does it sound plausible?

>
> The speed of light in water is less than it is in air. The effect is
> to longitudinally compress the geometry of light rays in front of the
> lens. Everything gets compressed, including the depth of field.
>
> As far as your question goes, the actual depth of field is reduced but
> the apparent depth of field is increased. I am sure that answer will
> leave you increasingly confused.

????
Indeed it does...!

Eric, can you provide some links/references/whatever on this subject?
Perhaps even a diagram of this 'longitudinal compression of light
rays' and how it then results in increased dof? Or a modified dof
formula, given the existing one has no refractive index component?
Surely, given the amount of specialised underwater cameras/lenses that
are out there, such a thing would exist...

Chrlz, Dec 30, 2009
8. ### Guest

On Dec 29, 7:34 am, (Harold keller) wrote:
> >>Someone once told me that one effect of photographing live fish in a
> >>glass aquarium is that the refractive index of the water somehow
> >>increases the depth of field.

>
> >>Has anyone else heard of this? Does it sound plausible?

>
> >The speed of light in water is less than it is in air. The effect is
> >to longitudinally compress the geometry of light rays in front of the
> >lens. Everything gets compressed, including the depth of field.

>
> >As far as your question goes, the actual depth of field is reduced but
> >the apparent depth of field is increased. I am sure that answer will
> >leave you increasingly confused.

>
> >Eric Stevens

>
> Do you mean it is reduced within the water, but appears greater from
> outside the aquarium/water?
>
> On a practical level, if my camera is outside of the aquarium, and I
> am photogrpahing fish swimming inside it, does the DOF become less
> critical, or increased,  in proportion to the refractive index of
> water?
>
> Harold Keller

I don't think it really matters much. The camera will see the same
thing your eyes are seeing, so it shouldn't be much of an issue.
I took a picture of a tank about three weeks ago and it was basically
point and shoot. Also took some HD video of it. That came out real
well.
Here is one example.. Not the greatest picture as I was just grabbing
a couple of snaps off it, but as you can see, the camera saw the same
thing my eyes did, so not much to worry about as far as taking
pictures
of it.
http://home.comcast.net/~disk100/fish.jpg

, Dec 30, 2009
9. ### MikeWhyGuest

wrote:
> On Dec 29, 7:34 am, (Harold keller) wrote:
>>>> Someone once told me that one effect of photographing live fish in
>>>> a glass aquarium is that the refractive index of the water somehow
>>>> increases the depth of field.

>>
>>>> Has anyone else heard of this? Does it sound plausible?

>>
>>> The speed of light in water is less than it is in air. The effect is
>>> to longitudinally compress the geometry of light rays in front of
>>> the lens. Everything gets compressed, including the depth of field.

>>
>>> As far as your question goes, the actual depth of field is reduced
>>> but the apparent depth of field is increased. I am sure that answer
>>> will leave you increasingly confused.

>>
>>> Eric Stevens

>>
>> Do you mean it is reduced within the water, but appears greater from
>> outside the aquarium/water?
>>
>> On a practical level, if my camera is outside of the aquarium, and I
>> am photogrpahing fish swimming inside it, does the DOF become less
>> critical, or increased, in proportion to the refractive index of
>> water?
>>
>> Harold Keller

>
> I don't think it really matters much. The camera will see the same
> thing your eyes are seeing, so it shouldn't be much of an issue.

The liquid/air interface refracts light and so acts as a lens, and so
changes the effective focal length. Anecdotally, wearing a mask or goggles
underwater without corrective lenses lessens the effect of my myopia. The
water serves to shorten the effective focal length. It would be good to see
an analysis.

MikeWhy, Dec 30, 2009
10. ### Eric StevensGuest

On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
<> wrote:

>On Dec 29, 6:39 pm, Eric Stevens <> wrote:
>> On Mon, 28 Dec 2009 20:36:02 GMT, (Harold
>>
>> keller) wrote:
>> >Someone once told me that one effect of photographing live fish in a
>> >glass aquarium is that the refractive index of the water somehow
>> >increases the depth of field.

>>
>> >Has anyone else heard of this? Does it sound plausible?

>>
>> The speed of light in water is less than it is in air. The effect is
>> to longitudinally compress the geometry of light rays in front of the
>> lens. Everything gets compressed, including the depth of field.
>>
>> As far as your question goes, the actual depth of field is reduced but
>> the apparent depth of field is increased. I am sure that answer will
>> leave you increasingly confused.

>
>????
>Indeed it does...!
>
>Eric, can you provide some links/references/whatever on this subject?
>Perhaps even a diagram of this 'longitudinal compression of light
>rays' and how it then results in increased dof? Or a modified dof
>formula, given the existing one has no refractive index component?
>Surely, given the amount of specialised underwater cameras/lenses that
>are out there, such a thing would exist...

Its not quite what you asked for but I found this:
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=378.0

Its fun but you need to be able to run JAVA

Eric Stevens

Eric Stevens, Dec 30, 2009
11. ### Chris MalcolmGuest

NameHere <> wrote:
> On Tue, 29 Dec 2009 21:39:08 +1300, Eric Stevens <>
> wrote:

>>The speed of light in water is less than it is in air.

> Which leads to the question, how can the speed of light ever be used as a
> mathematical constant? Since there's no such thing as a perfect vacuum,
> there's no such thing as the constant "C" known as the speed-of-light. It's
> all opinion, no matter which way you look at it.

It's not a mathematical constant, it's a physical constant. And the
same goes for all the fundamental basic constants of physics. Did you
go to one of those modern schools where they don't teach science?

--
Chris Malcolm

Chris Malcolm, Dec 30, 2009
12. ### ChrlzGuest

On Dec 31, 6:56 am, Eric Stevens <> wrote:
> On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
>
>
>
>
>
> <> wrote:
> >On Dec 29, 6:39 pm, Eric Stevens <> wrote:
> >> On Mon, 28 Dec 2009 20:36:02 GMT, (Harold

>
> >> keller) wrote:
> >> >Someone once told me that one effect of photographing live fish in a
> >> >glass aquarium is that the refractive index of the water somehow
> >> >increases the depth of field.

>
> >> >Has anyone else heard of this? Does it sound plausible?

>
> >> The speed of light in water is less than it is in air. The effect is
> >> to longitudinally compress the geometry of light rays in front of the
> >> lens. Everything gets compressed, including the depth of field.

>
> >> As far as your question goes, the actual depth of field is reduced but
> >> the apparent depth of field is increased. I am sure that answer will
> >> leave you increasingly confused.

>
> >????
> >Indeed it does...!

>
> >Eric, can you provide some links/references/whatever on this subject?
> >Perhaps even a diagram of this 'longitudinal compression of light
> >rays' and how it then results in increased dof?  Or a modified dof
> >formula, given the existing one has no refractive index component?
> >Surely, given the amount of specialised underwater cameras/lenses that
> >are out there, such a thing would exist...

>
> Its not quite what you asked for but I found this:http://www.phy.ntnu.edu..tw/ntnujava/index.php?topic=378.0
>
> Its fun but you need to be able to run JAVA
>
> Eric Stevens

Thanks, Eric, that's an interesting sim. I understand the magnifying/
foreshortening effect... but I'm intrigued on what sort of 'true',
measurable, depth of field change occurs.

It's interesting that the magnifying effect of water is often referred
to, and people with myopia (shortsightedness) report seeing better
underwater (eg, me..). But rectifying myopia, normally, requires a
*de*magnifying effect..

That does all suggest a true increase in perceived depth of field, and
underwater photography sites.. I'm just trying to tie this all
together a little more scientifically/mathematically.

Chrlz, Dec 31, 2009
13. ### Eric StevensGuest

On Wed, 30 Dec 2009 16:38:11 -0800 (PST), Chrlz
<> wrote:

>On Dec 31, 6:56 am, Eric Stevens <> wrote:
>> On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
>>
>>
>>
>>
>>
>> <> wrote:
>> >On Dec 29, 6:39 pm, Eric Stevens <> wrote:
>> >> On Mon, 28 Dec 2009 20:36:02 GMT, (Harold

>>
>> >> keller) wrote:
>> >> >Someone once told me that one effect of photographing live fish in a
>> >> >glass aquarium is that the refractive index of the water somehow
>> >> >increases the depth of field.

>>
>> >> >Has anyone else heard of this? Does it sound plausible?

>>
>> >> The speed of light in water is less than it is in air. The effect is
>> >> to longitudinally compress the geometry of light rays in front of the
>> >> lens. Everything gets compressed, including the depth of field.

>>
>> >> As far as your question goes, the actual depth of field is reduced but
>> >> the apparent depth of field is increased. I am sure that answer will
>> >> leave you increasingly confused.

>>
>> >????
>> >Indeed it does...!

>>
>> >Eric, can you provide some links/references/whatever on this subject?
>> >Perhaps even a diagram of this 'longitudinal compression of light
>> >rays' and how it then results in increased dof?  Or a modified dof
>> >formula, given the existing one has no refractive index component?
>> >Surely, given the amount of specialised underwater cameras/lenses that
>> >are out there, such a thing would exist...

>>
>> Its not quite what you asked for but I found this:http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=378.0
>>
>> Its fun but you need to be able to run JAVA
>>
>> Eric Stevens

>
>Thanks, Eric, that's an interesting sim. I understand the magnifying/
>foreshortening effect... but I'm intrigued on what sort of 'true',
>measurable, depth of field change occurs.
>
>It's interesting that the magnifying effect of water is often referred
>to, and people with myopia (shortsightedness) report seeing better
>underwater (eg, me..). But rectifying myopia, normally, requires a
>*de*magnifying effect..
>
>That does all suggest a true increase in perceived depth of field, and
>underwater photography sites.. I'm just trying to tie this all
>together a little more scientifically/mathematically.

A standard diagram of the way a camera works has rays of light coming
from the point of focus on the object and being bent where they pass
through the lens. Hopefully they are focussed to a point where they
meet the focal plane. I won't go into all the hoopla about depth of
field but in the real world it is theoretically possible to put in
markers at the front and rear edges respectively of the in-focus
field.

Now without changing the camera setup in any way, consider what
happens when you are photographing the inside of a fish tank through
its glass sides. The bending of the light rays as they leave the water
causes the point at which they focus on the object to be brought
closer to the camera. Yet, as far as the camera is concerned the rays
of light are still entering the lens at exactly the same angle as
before. But, if you put in markers at the front and back of the
in-focus field you will discover that they are both closer to the
camera and closer together than in the earlier situation when the
light rays were entirely through air.

If you then reach into the top of the tank with a pair of calipers or
similar and then measure their spread once you have got them out of
the water you will find the depth of focus is less than it was in air.
If the depth of field in air was (say) 10cm your calipers might tell
you (again, say) that the actual depth of field in water is only 8cm.
That's why I said "the actual depth of field is reduced".

If you now look at things from the point of view of the camera. The
light rays entering the camera still do so at the original angle and
the camera still thinks (do cameras think?) that the depth of field,
as it appears to the camera, is 10cm. But the actual depth of field
really is still only 8cm. That's why I said the "apparent depth of
field is increased" (over and above the actual depth of field). This
would be much easier to explain if I could draw a diagram.

Eric Stevens

Eric Stevens, Dec 31, 2009
14. ### NameHereGuest

On Thu, 31 Dec 2009 23:50:28 +1300, Eric Stevens <>
wrote:

>On Wed, 30 Dec 2009 16:38:11 -0800 (PST), Chrlz
><> wrote:
>
>>On Dec 31, 6:56 am, Eric Stevens <> wrote:
>>> On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
>>>
>>>
>>>
>>>
>>>
>>> <> wrote:
>>> >On Dec 29, 6:39 pm, Eric Stevens <> wrote:
>>> >> On Mon, 28 Dec 2009 20:36:02 GMT, (Harold
>>>
>>> >> keller) wrote:
>>> >> >Someone once told me that one effect of photographing live fish in a
>>> >> >glass aquarium is that the refractive index of the water somehow
>>> >> >increases the depth of field.
>>>
>>> >> >Has anyone else heard of this? Does it sound plausible?
>>>
>>> >> The speed of light in water is less than it is in air. The effect is
>>> >> to longitudinally compress the geometry of light rays in front of the
>>> >> lens. Everything gets compressed, including the depth of field.
>>>
>>> >> As far as your question goes, the actual depth of field is reduced but
>>> >> the apparent depth of field is increased. I am sure that answer will
>>> >> leave you increasingly confused.
>>>
>>> >????
>>> >Indeed it does...!
>>>
>>> >Eric, can you provide some links/references/whatever on this subject?
>>> >Perhaps even a diagram of this 'longitudinal compression of light
>>> >rays' and how it then results in increased dof?  Or a modified dof
>>> >formula, given the existing one has no refractive index component?
>>> >Surely, given the amount of specialised underwater cameras/lenses that
>>> >are out there, such a thing would exist...
>>>
>>> Its not quite what you asked for but I found this:http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=378.0
>>>
>>> Its fun but you need to be able to run JAVA
>>>
>>> Eric Stevens

>>
>>Thanks, Eric, that's an interesting sim. I understand the magnifying/
>>foreshortening effect... but I'm intrigued on what sort of 'true',
>>measurable, depth of field change occurs.
>>
>>It's interesting that the magnifying effect of water is often referred
>>to, and people with myopia (shortsightedness) report seeing better
>>underwater (eg, me..). But rectifying myopia, normally, requires a
>>*de*magnifying effect..
>>
>>That does all suggest a true increase in perceived depth of field, and
>>underwater photography sites.. I'm just trying to tie this all
>>together a little more scientifically/mathematically.

>
>A standard diagram of the way a camera works has rays of light coming
>from the point of focus on the object and being bent where they pass
>through the lens. Hopefully they are focussed to a point where they
>meet the focal plane. I won't go into all the hoopla about depth of
>field but in the real world it is theoretically possible to put in
>markers at the front and rear edges respectively of the in-focus
>field.
>
>Now without changing the camera setup in any way, consider what
>happens when you are photographing the inside of a fish tank through
>its glass sides. The bending of the light rays as they leave the water
>causes the point at which they focus on the object to be brought
>closer to the camera. Yet, as far as the camera is concerned the rays
>of light are still entering the lens at exactly the same angle as
>before. But, if you put in markers at the front and back of the
>in-focus field you will discover that they are both closer to the
>camera and closer together than in the earlier situation when the
>light rays were entirely through air.
>
>If you then reach into the top of the tank with a pair of calipers or
>similar and then measure their spread once you have got them out of
>the water you will find the depth of focus is less than it was in air.
>If the depth of field in air was (say) 10cm your calipers might tell
>you (again, say) that the actual depth of field in water is only 8cm.
>That's why I said "the actual depth of field is reduced".
>
>If you now look at things from the point of view of the camera. The
>light rays entering the camera still do so at the original angle and
>the camera still thinks (do cameras think?) that the depth of field,
>as it appears to the camera, is 10cm. But the actual depth of field
>really is still only 8cm. That's why I said the "apparent depth of
>field is increased" (over and above the actual depth of field). This
>would be much easier to explain if I could draw a diagram.
>
>
>
>Eric Stevens

LOL!!! And you think this doofus is going to understand what you just said?
The very same thing has already been explained at least 5 different ways.
You and I are being TROLLED.

But if you insist in a "diagram":

With water:

camera-> glass|water fish fish fish fish water|glass

No water

camera-> glass|air fish fish fish fish air|glass

replace "fish" in the second example with "dead fish" due to being only in
air, "fish" was only used to keep the ASCII spacing correct.

Reading USENET is like subjecting one's self to retarded kindergartner's.

NameHere, Dec 31, 2009